1. Field of the Invention
This invention relates to a clamping apparatus capable of temporarily firmly holding a work on e.g. a pallet in machining the work such as a cylinder block of an internal combustion engine and capable of easily releasing the work from the pallet after it has been machined.
2. Related Art
On a machining line of the work such as the cylinder block employed in the internal combustion engine of a motor vehicle, a transfer line is used in which a plurality of p processing machines arranged in order of machining steps are coupled by transfer devices and the work is transferred in order of the machining steps. On this transfer line, by fixing the work on the pallet and moving the pallet on the transfer line, the work is transferred in order of the machining steps and machined by the machining devices. In fixing the work on the pallet, a fluid-pressure spring clamping has been conventionally used which serves to detachably hold the work using oil pressure and spring elastic force.
Disclosed in JP-A-11-170133 is a conventional fluid-pressure spring clamping apparatus. The clamping apparatus includes a cylindrical piston member which vertically moves in a short stroke within a cylindrical clamping body, an output shaft which vertically moves in a long stroke within the piston member and projects from the clamping body, and a clamping arm attached to the tip of the output shaft and serving to clamp the work. Further, between the piston member and the clamping body, a tough spring member with a short stroke is arranged so that the piston member is urged in a direction of strongly clamping the work by the clamping arm through the output shaft. Further, between the output shaft and the piston member, a weak spring member with a long stroke is arranged.
Between the piston member and the output shaft, a locking mechanism is provided. Thus, in the vicinity of the position where the clamping arm clamps the work, the piston member and output shaft are locked by each other so that they are integrally moved within the clamping body. On the other hand, when the clamping arm leaves the clamping position of the work by a predetermined distance, the locking mechanism is unlocked so that the output shaft can be moved greatly within the piston member.
Between the clamping body, and the piston member and output shaft, a space filled with an operating oil is provided. By externally supplying or discharging the operating oil, the oil pressure can be exerted on the piston member and output shaft within the clamping body.
In the clamping apparatus of JP-A-11-170133, in releasing the clamping of the work, the operating oil is supplied to between the clamping body, and the piston member and output shaft so that the clamping is released by the oil pressure. In this case, the piston member and output shaft coupled with each other by the locking mechanism are integrally moved so that the above tough spring member is contracted to separate the clamping arm from the work by the short stroke. Next, the locking mechanism is unlocked so that only the output shaft is stroked within the piston member while the weak spring member is contracted by the oil pressure. Thus, the clamping arm is greatly separated from the work.
On the other hand, the work to be machined on the transfer line has different shapes and sizes according to car models when the work is the cylinder block for the internal combustion engine. So, the clamping position or moving direction of the clamping arm differs according to the height of the work clamping position from the pallet and its horizontal position, or the shape of the work around the clamping position.
In the clamping apparatus of JP-A-11-170133, however, because of the configuration described above, the clamping arm, piston member and output shaft cannot be easily dismantled. Therefore, when the work is replaced by another work, only the measure such as replacing the clamping arm can be taken. In this case, since the length of the output shaft remains unchanged, the great change in the clamping position in the height direction can be dealt with. In some clamping apparatuses, in separating the clamping arm from the work, the clamping arm is pivoted to facilitate the release of the work from the pallet. In this case also, however, the direction of pivoting cannot be changed by replacing the clamping arm.
Thus, by only replacing the clamping arm, as described above, the replacement of the work cannot be dealt with. As a result, in many cases, the pallet suited to the work must be newly provided. Accordingly, there were pallets corresponding to the kinds of the work.
Meanwhile, if the work is a heavy material such as the cylinder block, the weight of the pallet also necessarily increases. So where the work to be machined by the machining device is replaced, inconveniently, it takes a long time to replace the pallet on the transfer line. In addition, since the pallet is required for each model of the work, the place for keeping the pallets must be assured. Particularly, in the field having many kinds of works, inconveniently, it is difficult to assure the place for keeping the pallets.